Digital Elevation Model (AZ 7.5 - Minute)

7.5 Minute Digital Elevation Model for the state of Arizona. Digital Elevation Model (DEM) is the terminology adopted by the USGS to describe terrain elevation data sets in a digital raster form. The standard DEM consists of a regular array of elevations cast on a designated coordinate projection system. The DEM data are stored as a series of profiles in which the spacing of the elevations along and between each profile is in regular whole number intervals. The normal orientation of data is by columns and rows. Each column contains a series of elevations ordered from south to north with the order of the columns from west to east. The DEM is formatted as one ASCII header record (A-record), followed by a series of profile records (B-records) each of which include a short B-record header followed by a series of ASCII integer elevations per each profile. The last physical record of the DEM is an accuracy record (C-record). The DEM for 7.5-minute units correspond to the USGS 1:24000 scale topographic quadrangle map series for all of the United States and its territories. Each 7.5 minute DEM is based on 30- by 30-meter data spacing with Universal Transverse Mercator(UTM) projection. Each 7.5- by 7.5-minute block provides the same coverage as the standard USGS 7.5-minute map series.

亚利桑那州7.5弧分数字高程模型（Digital Elevation Model, DEM）。数字高程模型（Digital Elevation Model, DEM）是美国地质调查局（United States Geological Survey, USGS）所采用的术语，用于指代数字栅格格式的地形高程数据集。标准DEM由置于指定坐标投影系统下的规则高程阵列组成。该数据集以一系列剖面形式存储，每个剖面内部及剖面之间的高程间距均为规整的整数间隔。数据的常规排布采用行列结构：每一列包含一组由南至北排序的高程值，而列的排布顺序则为由西至东。该DEM的文件格式以一条ASCII头部记录（A记录）作为起始，随后跟随多条剖面记录（B记录）；每条B记录均包含一段简短的B记录头部，其后跟随对应剖面的一系列ASCII整数高程值。该DEM的最后一条物理记录为精度记录（C记录）。7.5弧分单元对应的DEM，与美国全境及海外领地所使用的美国地质调查局1:24000比例尺标准地形幅地图系列相匹配。每幅7.5弧分DEM均采用30米×30米的采样间距，并基于通用横轴墨卡托投影（Universal Transverse Mercator, UTM）。每幅7.5弧分×7.5弧分的图块，其覆盖范围与美国地质调查局标准7.5弧分地图系列完全一致。